Q: I caught my horse licking and eating dirt in her paddock. Is this normal? She’s currently on pasture all day and receives a ration balancer.

A:  It is not necessarily normal for horses to eat dirt, and trying to figure out why and how to stop horses from eating things we don’t want them to can be challenging. The term “pica” refers to persistent eating of nonnutritive substances for at least one month’s time and occurs in many animals. In some cases specific nutritional deficiencies can trigger unusual cravings, such as a long-term phosphorus deficiency causing cattle to eat bones or significant amounts of dirt. However, in horses these behaviors most often represent a normal physiological or foraging response.

Geophagia refers to eating dirt and is reported to be relatively common in feral and domestic horses. It is a behavior where horses actively bite or lick the ground to specifically eat dirt. Logic would suggest this to be a search for salt or minerals, but analysis of soils shows no consistent mineral profile of consumed versus nonconsumed soils. The soils tested varied tremendously in mineral content, although results from one study from Australia reported higher iron and copper in soil sites horses tended to consume. The challenge is domestic horses that are fed diets providing plenty of salt and minerals have also been seen consuming dirt, so geophagia is not simply a pursuit of minerals. 

Anecdotal evidence indicates dirt-eating might be more common in stallions than in mares or geldings, but no studies of gender effects on geophagia have been reported.  Surprisingly, a in 2016 study on colic risk factors, researchers in Egypt reported that horses practicing geophagia were less likely to have history of colic.

Although geophagia is generally considered harmless, excessive consumption of sandy soil, and particularly accumulation of sand in the digestive tract, can lead to mucosal irritability and potentially obstruction or motility disorder. Some horses are more prone to eating or accumulating sand than others, even when eating the same diet under the same conditions. Grazing pastures on sandy soil, lower herd hierarchy, inadequate forage consumption, feeding grain on the ground, and low body condition and young age are all factors that might contribute to increased sand ingestion. Both stall confinement and frequent transportation might also be contributing factors to accumulation of ingested sand due to reduced gut motility.

If you observe a horse exhibiting unusual eating behaviors such as geophagia, evaluate the nutritional balance of the diet, the availability of ample roughage, and the general environment for potential causes of the behavior. A veterinary exam to detect parasite infestation or gastric or other health issues might also be warranted. If the diet is adequate, the horse is healthy, and other factors are not at play, then it might be a simple case of boredom or acquired taste. Decreasing time spent in confinement, providing a companion, and increasing exercise might help alleviate the problem.